Method for threading a string through HVAC ducts

ABSTRACT

The invention is a method for threading a thin string through an HVAC duct system from a vent to the HVAC equipment supply plenum where the vent is connected to a small supply duct which in turn is connected to a large supply trunk connected to the plenum. The method uses a high speed blower at the vent to propel a small resistance object connected to the string through the small duct until it reaches the trunk. Then a capture mechanism is used from the HVAC plenum to capture the object and pull the string to the plenum. In an example of the method, the resistant object includes a packed parachute that is released after it travels a predetermined distance.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to HVAC zone control systems for retrofit, and specifically to methods for threading air tubing and wires through concealed HVAC duct systems.

2. Background Art

Most zone control systems for HVAC systems use electromechanical dampers to selectively control the airflow through portions of the trunk and duct system. Installation of these zone systems requires access to the ducts at multiple locations so that the dampers can be installed. However, in many building the ducts are not easily accessible because they are embedded in walls, ceilings, and floors. Even when a duct is accessible for damper installation, there may no be a clear path to run control wires outside the duct from the damper to the control system. In nearly all cases, the interior of the duct system provides a path from each vent to the central HVAC equipment. The existing ductwork can be used as a conduit for running control wires or air tubes from the vents to the HVAC equipment. This requires a practical method for threading the wire or air tube from the damper to the HVAC equipment.

U.S. Pat. No. 6,786,473 issued Sep. 7, 2004 to Alles, U.S. Pat. No. 6,893,889 issued Jan. 10, 2004 to Alles, U.S. Pat. No. 6,997,390 issued Feb. 14, 2006 to Alles, U.S. Pat. No. 7,062,830 issued Jun. 20, 2006 to Alles, U.S. Pat. No. 7,162,884 issued Jan. 16, 2007 to Alles, U.S. Pat. No. 7,188,779 issued Mar. 13, 2007 to Alles, and U.S. Pat. No. 7,392,661 issued Jul. 1, 2008 to Alles, describes various aspects of a HVAC zone climate control system that uses inflatable bladders. The present invention is by the same inventor and is designed to be used when installing this system. However, the invention has more general application and can be used to thread wire or tubing through duct work for any purpose.

This system describes it these patents has multiple inflatable bladders installed in the supply ducts such that the airflow to each vent can be separately controlled by inflating or deflating the bladder in its supply duct. Each bladder is connected to an air tube that is routed from each vent through the duct and trunk system back to a centrally located set of computer controlled air valves that can separately inflate or deflate each bladder. Based on temperature readings from each room and the desired temperatures set for each room, the system controls the heating, cooling, and circulation equipment and inflates or deflates the bladders so that the conditioned air is directed where needed to maintain the set temperatures in each room.

U.S. Pat. No. 7,062,830 issued Jun. 20, 2006 to Alles describes a method of installing the air tubes. This method uses air flow from the vent toward the HVAC equipment to pull a parachute and thin string from the vent to the HVAC equipment. At the HVAC equipment, an air tube is connected to the string and the string is pulled toward the vent until the air tube reaches the vent. This method requires all vents but one be blocked so that all of the airflow generated by a blower at the HVAC system comes from one vent. This method works well for many duct systems and specific duct paths. However, this method does not work well for certain duct systems and paths.

Excessive duct leakage can prevent this method from working. With all vents sealed but one, all of the airflow generated by the blower should flow through the one open vent. However, leaks in the duct system can also supply some of the airflow. If the leakage is excessive, there is insufficient airflow at the vent to inflate and pull the parachute.

Small supply ducts at the vent in the range of 4″ to 6″ in diameter can prevent this method from working even with strong airflow. In a small vent, a large portion of the parachute is in contact with the walls of the duct creating significant friction, and making it more likely screws or sharp edges will snag the parachute. In addition, the airflow in the small cross-section area produces a small force on the parachute. Increasing the air flow to increase the pulling force also increases the friction since the parachute is pushed harder against the duct walls. The combination of significant friction and a small force makes it difficult for the parachute to pass through the duct.

If a smaller parachute is used for smaller ducts, it is often easier for the parachute to pass through the duct. However, the small duct eventually connects to a larger duct or main supply trunk. As the duct cross-section increases, the air velocity decrease and the small parachute can not product enough force to pull the string to the HVAC equipment.

In some duct networks with long duct runs with many turns, the resistance between the string and the duct walls become excessive as the length of the string being pulled increases. The force generated by the parachute is not sufficient to overcome the string pulling friction.

OBJECTS OF THIS INVENTION

An object of this invention is to provide an improved method for threading a string through an HVAC duct system from a vent to the HVAC equipment where a small duct supplies the vent and the small duct is connected to a large supply trunk connected to the HVAC supply plenum.

Another object is to provide an improved method of threading string that is compatible with the tools and training used to thread string using the methods of the prier art.

Another object is to provide an improved method of threading string that is more predictable for a wider variety of duct systems than the methods of the prier art.

SUMMARY

The invention is a process for threading a thin string through an HVAC duct system from a vent to the HVAC supply plenum where the vent is connected to a small supply duct which in turn is connected to a large supply trunk connected to the plenum. The method uses a high speed blower at the vent to propel a small resistance object connected to the string through the small duct until it reaches the trunk. Then a mechanism is used from an access in the plenum to capture the resistance object and pull the string to the plenum. The capture mechanism can be a hose, rod, tube, or pipe for pushing one of a hook, snag tool, or source of vacuum pushed into the trunk through the access to reach the object. The mechanism captures the object which is then pulled back to the access in the plenum. In a variation of the method, the resistant device includes a packed parachute that is released after it travels a predetermined distance. After the resistance object is pushed through the small duct to the trunk by the high speed blower, the parachute unpacks and airflow generated by a blower at the plenum access pulls the parachute and string to the HVAC equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood more fully from the detailed description given below and from the accompanying drawings of embodiments of the invention which, however, should not be taken to limit the invention to the specific embodiments and methods described, but are for explanation and understanding only.

FIG. 1 is a perspective view of a HVAC system with tools for threading a string.

FIG. 2A is the outline of a snag tool.

FIG. 2B is a perspective view of the stag tool attached to segment of pipe.

FIG. 3A is a perspective view of the spool of the two-state object.

FIG. 3B is a cross-section view of the spool of the two-state object.

FIG. 3C is a perspective view of the assembled components of the two-state object in the parachute state.

FIG. 3D is a perspective view of the preparation of the two-state object for setting to the ball state.

FIG. 3E is a perspective view of the two state-object in the ball state.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of portion of a typical HVAC system found in residential dwellings. HVAC equipment 100 includes a fan for generating a flow of warmed or cooled air through a network of supply ducts that distribute the air throughout the dwelling. The duct network includes a main trunk 101 connected to the supply plenum of the HVAC equipment 100. Only a small section of the main trunk is shown. The open end 102 is connected to the remainder of the duct network. A smaller duct 104 connects to the main trunk at 107 and provides a path for airflow to vent 105. There are one or more such vents in each room of the dwelling. Each of the other vents is connected to a smaller duct that also connects to the main trunk. A typical dwelling has 10 to 30 vents; only one vent of many is shown in FIG. 1. Air is returned to the HVAC equipment through duct 103 which is connected to one or more large centrally located return vents in the dwelling. In many dwellings, the duct network is enclosed by walls, floors, and or ceilings. Easy access is only available at the vents and at the supply plenum. An access hole 106 cut in the supply plenum near the HVAC equipment provides the only needed access to the interior of the main trunk 101 used in the method of this invention.

Using the method of the prier art to thread a string from vent 105 to plenum access 106, a suction blower 130 is connected to trunk access 106 by flexible hose 133 and flange 131. The air pulled from the duct network through the access 106 is discharged through vent 132 of blower 130. All vents are sealed to block airflow except for vent 105. Airflow through return 103 is also blocked. This configuration maximizes the airflow from vent 105 to plenum access 106. A parachute 112 connected to string 113 is inserted in vent 105 and the airflow propels the parachute through duct 104 to trunk 101 and to access 106.

However, the airflow is limited by the capacity of the blower 130, the air resistance of duct 104, and the air leakage of the entire duct network. In some cases, the airflow generated at vent 105 is insufficient to pull the parachute 112 of the prier art method through the small duct. In other cases, the air pressure that inflates the parachute causes the parachute to cling tightly to the duct walls, increasing the friction between the parachute and the duct. The force generated on the parachute by the airflow may be insufficient to overcome the friction between the parachute and duct. The force holding the parachute to the duct walls also increases the chances of snagging the parachute on screws and seams inside the duct. Using a small parachute reduces snagging and friction, but does not provide sufficient air resistance to pull the string once the parachute reaches trunk 101.

In the general method of this invention, the airflow produced by blower 130 is augmented by a high velocity blower 110 at vent 105. Electric leaf blowers available from several manufactures are suitable for generating the required high velocity airflow. For example, Model BV4000 supplied by the Black and Decker Corporation, 701 East Joppa Road, Towson, Md. 21286. The airflow generated by the leaf blower 110 at vent 105 is sufficient by itself to propel a parachute from the vent to the main trunk. After the parachute reaches the main trunk at 107, the airflow generated by blower 130 pulls the parachute to the access 106. When using the method of this invention, it is preferable to leave the vents upstream of connection 107 unsealed so that airflow is maximum in trunk 101 from connection 107 to access 106. Vents down stream of duct connection 107 (none shown in FIG. 1) should be closed.

In some situations the duct 104 has many screws or other obstructions that prevent parachute 112 of the prier art method from traversing the length of 104 to connection 107, no matter the volume or velocity of airflow generated by leaf blower 110. A variation of the method of this invention is to replace the function of parachute 112 with a light object 120 of fixed shape small enough to easily fit inside duct 104. In the preferred method, the object is a ball made from expanded polystyrene foam commonly referred to as Styrofoam, a registered trademark of the Dow Chemical Company, 2030 Dow Center, Midland, Mich. 48674. These balls are supplied by many arts & crafts retail stores or can be easily shaped by hand from bulk material. Typically a 2″ diameter ball is used for 4″ ducts and a 3″ ball used for ducts larger than 5″. The ball 120 is tied to string 121 and the ball is placed through vent 105 into duct 104. Leaf blower 110 is then used to propel the ball and string through duct 104 to connection 107 and into the trunk 101.

The airflow in trunk 101 generated by blower 130 is insufficient to propel the ball 120 to access 106. A variation of the method of this invention uses a capture mechanism that can be pushed by the installation technician from access 106 into trunk 101 to the connection 107. The technician uses the mechanism to capture the ball and/or string and then pull the string 121 to the access 106. Several different capture mechanisms are suitable for this function. The preferred mechanism depends on the duct network, the availability of the mechanism during the installation process, and the skill of the technician.

One example of a suitable capture mechanism is an apparatus specifically designed for duct cleaning. Many HVAC contractors have duct cleaning equipment and are skilled in its use. One example of suitable equipment is the Rotobrush aiR+ model supplied by Rotobrush, 801 Hanover Drive, Suite 700, Grapevine, Tex. 76051. Other examples include the Maverick and the Renegade models supplied by Extraction Systems International, 5330 Derry Avenue, Suite D, Agoura Hills, Calif. 91301. This equipment has a brush connected to a hose that is suitable for pushing through trunk 101. The technician can manipulate the brush to wrap the string and ball around its hose. The technician can then pull the hose back to the access 106, pulling the string along.

Another example of a suitable capture mechanism is fish tape commonly used by electricians to pull electrical wires through conduit. Fish tape is available through distributors serving the electrical trade and retail home improvement stores. The fish tape can be bent at one end to form a hook suitable for hooking the string 121. The technician manipulates the fish tape through access 106 and trunk 101 until string 121 can be hooked. The ball 120 prevents the string from slipping through the hook. The technician then pulls the fish tape and string back to access 106.

Another example of a suitable capture mechanism is a vacuum cleaner connected to a vacuum hose suitable for pushing down trunk 101. The hose is pushed through access 106 and trunk 101 to the vicinity of ball 120. The vacuum is then turned on and the hose manipulated until the ball is captured and held by the vacuum and the hose. The hose with the ball firmly held by the vacuum is then pulled back through access 106, pulling the string 121 along.

Another example of a suitable capture mechanism can be assembled from sections of semi-rigid rod, tube, or pipe. A suitable semi-rigid rod is called a push-pull rod routinely used by electricians to pull wires through walls, floors, and ceilings. These are supplied in short lengths that can be assembled to make a rod over 30′ long. Another suitable semi-rigid rod is a telescoping pulling pole also used by electricians. These poles are 2′ to 3′ long when collapsed and 16′ to 26′ feet long when extended. Push-pull rods and telescoping pulling polls are available from most distributors serving the electrician trade. Suitable semi-rigid pipes or tubes include ¾″ PVC water pipe and electrical conduit.

A semi-rigid mechanism is suitable where the distance from access 106 to connection 107 is beyond the convenient reach of pushing a flexible hose used by the mechanisms described in the foregoing. FIG. 2A is the outline of snag tool 200 cut from 28 gauge sheet metal of the type used to fabricate HVAC duct work. Typically the snag tool is about 2″ long and 1″ wide. After cutting the outline shape, the points 201, 203, and 205 are bent downward about 20 degrees into the plane of the drawing. Points 202, 204, and 206 are bent upward about 20 degrees out of the plane of the drawing.

FIG. 2B is a perspective diagram of the snag tool attached to a section of PVC water pipe 210. The snag tool is held in place using tape 211 wrapped around the pipe 210 and end 207 of the snag tool 200. The snag tool can be similarly attached to any of the semi-rigid rods, tubes, or pipes described in the foregoing.

Referring to FIG. 1, typically sections of PVC pipe 3′ long can be inserted into the trunk 101 through access 106. Successive sections of PVC pipe can be coupled to the end opposite the snag tool as the pipe assembly is pushed down the trunk. When the assembled pipe is long enough to reach the connection 107, the technician positions the snag tool next to the string 121 rotates the pipe to wrap the string around the snag tool. The pipe is then disassembled as it is pulled from the trunk. The method is similar for any semi-rigid rods, tubes, or pipes that can be assembled within trunk 101.

Another variation of the method of this patent uses a two-state object that combines the properties of ball 120 the parachute 112 of the method of the prier art. The ball-state of the object has the properties of a ball while in duct 104 and the parachute-state has the properties of a parachute when in the trunk 101. The object makes the transition from the ball-state to the parachute-state after traveling a settable pre-defined distance. The distance is set to be slightly longer than the total length of duct 104. Leaf blower 110 propels the object in the ball-state through duct 104 until it reaches connection 104. After the object transitions to the parachute-state, airflow generated by blower 130 pulls the object to the access 106.

FIG. 3 shows various aspects of the preferred embodiment for the two-state object. FIG. 3A is a perspective diagram of a bobbin or spool suitable for winding a parachute and a length of string. FIG. 3B is a cross-section view of the spool through its rotation axis. The spool is made of expanded polystyrene foam. The ball 121 described in the foregoing can be easily shaped by hand to function as the spool shown in FIG. 3A. The grove 301 can be made in the spherical surface 302 using the fingers to pinch foam away around a circumference and then smoothed using finger pressure to compress the rough foam into the grove.

FIG. 3C is a perspective view of the assembled two-state object in the parachute-state. The parachute canopy 310 is shown released and fully inflated. Four strings 311 are connected to the four quadrants of the canopy's edge and connect to the string 312 that is threaded between vent 105 and access 106. Spool 300 is tied to string 314. The length of string 314 is about equal to the sum of the length of strings 311 and half the circumference of canopy 3 10. When the parachute is in trunk 101 as shown in FIG. 1 and inflated by the airflow produced by blower 130, there is sufficient force on the parachute to pull string 312 from the vent 105 and pull the spool 300 along by string 314.

FIG. 3D shows the components of the two-state object ready for assembly into the ball-state. The parachute canopy 310 is deflated, flattened, and smoothed to be a compact as possible. The components are aligned as shown in FIG. 3D and the slack in string 314 is wound on spool 300 until the tip of canopy 310 touches spool 300. The collapsed canopy 310 and strings 311 are then would onto the spool along with string 314. A length of string 312 longer than the length of duct 104 in FIG. 1 is then wound on the spool over the parachute canopy 310 and strings 311.

FIG. 3E is a perspective view of the two-state object assembled into the ball-state. Parachute canopy 310 is held firmly in place by multiple windings string 312. When the assembled two-state object is placed in duct 104 in FIG. 1, it behaves similar to the ball 120 described in the forgoing. Leaf blower 110 produces sufficient air velocity and airflow volume to propel the object through the duct. The string 312 unwraps from the spool 300 as the object is pushed through the vent. The parachute is held tightly to the spool until the string is completely unwound. The parachute is released as it unwinds from the spool. Since the string 312 wound around spool 300 is slightly longer than duct 104, the parachute is deployed inside trunk 101. If the string 312 is not completely unwound when the object reaches the trunk 101, the technician at vent 105 can pull string 312 back while using the leaf blower to create airflow. As the object is pulled to connection 107, the airflow from duct 104 will exert a force on the object causing the string to unwind and/or the parachute to inflate. Likewise, if the object encounters an obstruction in the duct 104, the technician can manipulate the string 312 to cause the object to jump or move to a different portion of the duct, thereby clearing the obstruction.

An additional benefit of unwinding string 312 from the spool 300 as it is propelled through duct 104 is the elimination of the pulling friction between the string and the duct.

In the method of the prior art, the force generated by the parachute must pull the string from the vent through the duct. The string is supplied from the vent. The string pulling resistance increase as the travel length increases and with addition turns in the duct path. For long ducts with many turns, the parachute can not generate sufficient force to pull additional string from the vent. When the object caries the string and unwinds the string as it is propelled, the required force to propel the object does not depend on the length of string unwound in the duct or the number of turns in the duct.

Conclusion

From the forgoing description, it will be apparent that there has been provided an improved method for threading a string from a vent to a central plenum of a HVAC system. Variation and modification of the described method, tools, and objects will undoubtedly suggest themselves to those skilled in the art. Accordingly, the forgoing description should be taken as illustrative and not in a limiting sense.

The various features illustrated in the figures may be combined in many ways, and should not be interpreted as though limited to the specific embodiments in which they were explained and shown. Those skilled in the art having the benefit of this disclosure will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the present invention. Indeed, the invention is not limited to the details described above. Rather, it is the following claims including any amendments thereto that define the scope of the invention. 

1. In a forced air HVAC system having a network of air ducts connecting a central supply plenum to a plurality of air vents, a method for threading a string from at least one of said air vents to said plenum, comprising: a. providing a light weight resistance object that easily fits inside the duct connected to said one of air vents, said duct being in said network; b. connecting said object to a string; c. providing a blower at one of said vents; d. using said blower to propel said object from one of said vents through said duct to where said duct connects to a large duct of said network; e. providing at said plenum a capture means for pushing into said network and capturing said object; f. pushing said capture means into said plenum and said network toward said object; g. capturing said object; h. pulling said object and said string back to said plenum; thereby threading said string from one of said vents to said plenum.
 2. The method of claim 1 where said object approximates the shape of a sphere.
 3. The method of claim 1 where said object approximates the shape of a sphere and is composed of foam plastic.
 4. The method of claim 1 where said capture means is a semi flexible element suitable for pushing with a snag tool attached to one end of said element.
 5. The method of claim 1 where said capture means is a semi flexible hose suitable for pushing, said hose attached to a source of vacuum airflow.
 6. The method of claim 1 where capture means is an apparatus for cleaning ducts.
 7. In a forced air HVAC system having a network of air ducts connecting a central supply plenum to a plurality of air vents, a method for threading a string from at least one of said air vents to said plenum, comprising: a. providing a light weight object with two resistance states that easily fits inside the duct connected to said one of air vents, said duct being in said network; b. connecting said object to a string; c. providing a blower at one of said vents; d. using said blower to propel said object in low resistance state from one of said vents through said duct to where said duct connects to a large duct of said network; e. providing at said plenum a vacuum blower; f. connecting said vacuum blower to said plenum and creating an airflow toward said plenum; g. providing a means for said object to transition to high resistance state; h. allowing said object and said string to be pulled back to said plenum by said airflow; thereby threading said string from one of said vents to said plenum.
 8. The method of claim 7 where said object includes a packed parachute with a means for controlling unpacking of said parachute.
 9. The method of claim 7 where said object is a packed parachute with a mechanism that unpacks said parachute after a predetermined distance traveled in said duct.
 10. The method of claim 7 where said object is a combination of a parachute and a spool suitable for winding said parachute and a length of string into a shape suitable for rolling, said length of string being longer than the length of said duct.
 11. In a forced air HVAC system having a network of air ducts connecting a central supply plenum to a plurality of air vents, a method for threading a string from at least one of said air vents to said plenum, comprising: a. providing a light weight resistance object that easily fits inside the duct connected to said one of air vents; b. winding a length of string onto said object; c. providing a means for generating an airflow from one of said vents to said plenum; d. using said airflow to propel said object from one of said vents through said network and unwinding said length of string in said network as said object is propelled; e. recovering said object at said plenum; thereby threading said string from one of said vents to said plenum.
 12. The method of claim 11 where said airflow is generated by a combination of a blower at one of said vents and a blower at said plenum.
 13. The method of claim 11 where said resistance object approximates the shape of a sphere.
 14. The method of claim 11 where said object approximates the shape of a sphere composed of foam plastic.
 15. The method of claim 11 where said object has a low air resistance state and a high air resistance state.
 16. The method of claim 11 where said object has a low air resistance state and a high air resistance state, and is in said low resistance state when at said one of vents, and transitions to said high resistance state after being propelled a predetermined distance in said network. 